The primary aim of the research I have undertaken is to better understand the influence of dopamine on behavior and to build on knowledge of the various roles of dopamine in the healthy brain but also to improve understanding of the deficits affecting patients with Parkinson’s disease (PD), the hallmark of which is dopamine depletion. By testing PD patients on cognitive and motor tasks, we are able to probe the effects of dopamine depletion in humans. Testing PD patients in different medication states also provides a method with which to attempt to tease apart the various roles of dopamine from each other. My first two experiments use the PD model to this end whereas the third experiment utilises a pharmacological manipulation in healthy individuals. The aim of my first experiment was to tease apart the relative contribution of dopamine to learning from its influence on action performance, and by doing this to better understand the deficits which have been observed in PD patients in reinforcement learning tasks. The second experiment focuses on the motor deficits observed in PD. The aim of this study was to test whether these motor deficits can at least in part explained by the deficits in reward sensitivity. The third and final experiment in this thesis uses a pharmacological manipulation in healthy individuals to isolate the role of dopamine in set shifting in the context of a response to cues with negative hedonic valence, with the hope of better understanding the neurobiology underlying pathological behaviours associated with the hyperdopaminergic state.